libgui: Plumb detachBuffer through ConsumerBase

Exposes IGraphicBufferConsumer::detachBuffer as a ConsumerBase
method. attachBuffer is not currently exposed, because all current
clients will be recycling buffers through the allocator.

Bug: 19628705
Change-Id: I3e519767fa43d5d880c1d5695e31b60f6ad588af
2 files changed